1. Field of the Invention
The present invention relates to flow control units adapted to permit the flow of a fluid in a controlled manner. More particularly, this invention is directed to a flow control panel which directs a flowing fluid medium through a plurality of passages and which is capable of adjusting the flow rate of the flowing fluid medium. Such a flow control panel may be used as a heat exchanger, an evaporator or similar apparatus.
2. Description of the Related Art
Various attempts have been made to cause a fluid to flow over a flat sheet or through a panel. For example, Japanese laid-open utility model publication No. 7-41267 discloses a flat tubing which includes a guide made of a fibrous material and adapted to allow a flowing fluid medium to flow therethrough, and pressure control passages defined at opposite sides of the guide passage. However, a disadvantage with the tubing is that the air tends to remain in the guide. This results in uneven flow of the fluid.
Japanese laid-open patent publication No. 8-61784 discloses a flow control panel (see FIG. 19) which generally includes a flat substrate, an intermediate, hydrophilic layer attached to the substrate, and a plurality of partitions attached to the intermediate layer and arranged in parallel. By this arrangement, a plurality of fluid passages are defined on the intermediate layer between adjacent partitions. The partitions, typically made of resin, are attached to the intermediate layer by application of pressure and heat. However, the resin is likely to enter the fluid passages while the pressure is being applied to the partitions. This results in a decrease in the cross sectional area of the passages and thus, impedes or limits the flow of a fluid through the passages.
Japanese utility model publication No. 7-8996 discloses an improved flow control panel (see FIGS. 20 and 21) designed to allow a relatively large amount of fluid to flow through passages in a controlled manner. To that end, a cover sheet is secured to the free ends of partitions and expandable so as to prevent the internal pressure of the passages from increasing. However, after repeated use, the cover sheet often becomes elongated as a result of thermal expansion. Such elongation also occurs where a vacuum is created in the bottom of the passages as a result of a reduced flow rate. Slackening of the cover sheet results, as seen in FIG. 21. Another problem is that the cover sheet tends to be attached to the substrate under the influence of a fluid remaining in the passages. Consequently, the passages partly closes. In the case that the panel is used as a heat exchanger, slackening of the cover sheet and closing of the passages deteriorate the heat exchange or heat transfer capability of the panel. The panel is also susceptible to vertical loads which can also cause changes in the cross sectional area of the passages. Such changes prevent the flow rate of a fluid from being adequately controlled.
Accordingly, it is an object of the present invention to provide a flow control unit wherein the effective cross sectional area of passages can be varied in response to a change in the flow rate of a fluid flowing through the passages to thereby accommodate changes in the internal pressure of the passages.
It is another object of the present invention to provide a flow control unit which includes permeable partitions or pressure relief means to provide a fluid communication between adjacent passages.
It is a further object of the present invention to provide a flow control unit which is durable, economical and easy to manufacture.